In order to obtain your password, you must return to the site that you originally signed-up for and click on the "Forgot Password?" link found on the login page...
If you aren't receiving your password via email, be sure to check your email account's spam folder*...
* GMail's ‘Spam' folder is hidden from view by default. To view the folder, simply hover your mouse pointer over any of the folder names in the left column of the GMail user interface: the column will expand to show all the folder labels, including the ‘Spam' folder.